This invention relates generally to advances in medical systems and procedures for prolonging or improving human life. More particularly, this invention relates to an improved method and system for alleviating urinary obstruction caused by enlargement of the prostate by performing thermal ablation for urethral enlargement.
A majority of all males over 60 years old experience partial or complete urinary obstruction because of enlargement of the prostate. This condition usually originates from benign prostatic hyperplasia (BPH), which is an increase in cell mass near the urethra, or less likely, from prostate cancer. Both these conditions involve an increase in prostatic tissue mass, which in its increased state encroaches on the urethra and obstructs the urinary pathway.
In the case where urinary obstruction is caused by BPH, a common treatment involves a medical procedure using a medical side-cutting instrument and/or endoscope to surgically enlarge a passageway for urine flow through the prostate. The side-cutting instrument or an endoscope is passed through the penis into the urethra and is surgically used to remove prostate tissue and part of the urethra at the point of obstruction. This procedure is referred to as xe2x80x9cTrans-urethral Resection of the Prostatexe2x80x9d (or xe2x80x9cTURPxe2x80x9d).
This procedure, although effective, is invasive and complicated. For example, it requires the use of anesthesia and substantial hospital care. It also has the risk of causing bleeding. Moreover, it is expensive and causes great discomfort and trauma to the patient. For example, chapter 18, entitled xe2x80x9cComplications of Transurethral Resection of the Prostate,xe2x80x9d by R. Sunshine and M. Droller, of a book entitled Urologic Complications, Medical and Surgical, Adult and Pediatric, edited by Fray S. Marshall (Yearbook Medical Publishers, 1986), elaborates on the various complications of the TURP procedure.
In the case where urinary obstruction results from prostatic cancer, surgical prostatectomies are commonly used to eliminate the obstruction. However, surgical prostatectomies have serious side effects and risks, including impotence and urinary incontinence.
In recent years, less invasive systems and procedures that inflict less trauma on patients have been attempted. One such procedure, called xe2x80x9cTrans-urethral Needle Ablationxe2x80x9d (or TUNA), involves passing a radio-frequency (RF) instrument such as a catheter, cannula, sheath, or scope into the urethra. The RF instrument houses special RF electrode tips that emerge from the side of the instrument. The tips are pushed out of the instrument along off-axis paths to pierce the urethral wall and pass into the prostatic tissue outside of the urethra. As a result of the various electrodes emerging from the side of the instrument, such radio-frequency instruments are frequently complex and expensive.
By heating the prostate with RF power applied through the electrode tips emerging from the side of the radio-frequency (RF) instrument, the prostate tissue surrounding the urethra is ablated. Specifically, heat ablation is performed at multiple locations outside the urethra to provide a series of ablations, thereby causing the prostate tissue outside the urethra to die and necrose. Subsequent to heating, the necrotic tissue is absorbed by the body or excreted, thereby reducing the tissue mass outside the urethra, which consequently reduces the urethral obstruction.
For further explanation of this system and procedure, one can consult a research paper published by Goldwasser et al., entitled xe2x80x9cTransurethral Needle Ablation (TUNA) of the Prostate Using Low-Level Radio-Frequency Energy: an Animal Experimental Studyxe2x80x9d; Eur. Urol., vol. 24, pp. 400-405 (1993); and a research paper published by Schulman, et al., entitled xe2x80x9cTransurethral Needle Ablation (TUNA); Safety, Feasibility, and Tolerance of a New Office Procedure for Treatment of Benign Prostate Hyperplasma;xe2x80x9d Eur. Urol., vol. 24, pp. 415-423 (1993). Also, product literature on the TUNA system available from a company named Vitamed, Inc., of Menlo Park, Calif., carries some description of the procedure.
The TUNA system and procedure is generally used to relieve urethral obstruction caused by BPH. It favors a transurethral approach because the target tissue to be ablated is generally near to it. However, again, although the TUNA system and procedure is effective, it requires epidural or general anesthetic, and generally causes the patient great discomfort and pain. Moreover, the TUNA procedure is medically and technically very complex for surgeons to perform, requiring a complicated and expensive catheter or sheath or RF electrode system to perform it. Also, it is a relatively blind procedure in the sense that the ends of the RF electrodes emerging at the side of the radio-frequency electrode system, once they penetrate the target tissue, cannot be seen. Nor is there any technique for providing a visual representation of them. Furthermore, the TUNA system and procedure attempts to leave the urethra intact and uninjured by the application of RF heating, which is difficult to achieve, making its outcome uncertain. The TUNA system and procedure causes scratching of the urethra, bleeding or irritation from a cystoscope, cannula, catheter, or tissue-piercing electrode tips passed into the urethra. Furthermore, the TUNA procedure produces trapped coagulated and necrotic tissue or fluid in the interstitial region of the prostate outside the urethra. This can result in swelling and increased pressure of tissue outside the prostate as the necrotic tissue is absorbed by the body. Such pressure can compress the urethra to further enhance its obstruction.
Another system and procedure contemplated by Onik et al. is described in their research paper entitled xe2x80x9cA Transrectal Ultrasound-Guided Percutaneous Radical Cryosurgical Ablation of the Prostate,xe2x80x9d Cancer, vol. 72, pp. 1291-1299 (1993). This technique is utilized for the treatment of prostate cancer and involves disposing cryogenic (freezing) probes in the prostate for ablating the cancer cells. Onik et al. propose passing a cryogenic probe transperineally (through the perineum) into the prostate. At the same time, an imaging ultrasonic probe is passed through the rectum and is used to visualize the position of the cryogenic probe and the volume of cryogenic ablation in the prostate. This technique requires use of cryogenic probes (also referred to as cryo-probes) having relatively large diameters. The cryo-probes are complex in construction and operation and require elaborate cooling and thawing cycles, making the procedure typically quite complicated and expensive. It is technically challenging and critical to maintain precise temperatures at the target tissue area to prevent hemorrhaging when removing the probe and also to prevent freezing sensitive rectal mucosa tissue.
One more recent procedure contemplated and reported by McGahan, et al., in their research paper entitled xe2x80x9cPercutaneous Ultrasound-Guided Radio-frequency Electrocautery Ablation of Prostate Tissue in Dogs,xe2x80x9d Acad. Radiol., pp. 61-64 (1994), involves placing an RF electrode transrectally into the prostate of a dog under rectal ultrasound guidance. Their intent was solely to explore the feasibility of ablating cancerous tumors within the peripheral region of the prostate. Their research treated only normal animals and no ablation of cancer tissue was actually performed. McGahan et al. hoped to prevent RF heat ablation of the urethra (which is located centrally in the prostate). To achieve their objective, they suggested that the urethra should be irrigated with saline solution, using a catheter, to prevent RF heat damage to the urethra and periurethral tissue. They concluded that their system and procedure was impractical for ablating prostate cancer cells, because the RF lesions were limited to 1 to 1.5 cm in diameter, which they felt would be too small to adequately treat malignant cancer cells.
Generally, prostate cancer primarily occurs in the peripheral (non-central) zone of the prostate. It is often multi-focal, near the rectal wall, and near nerves controlling potency. Recognizing the restraints and delicate circumstances, McGahan et al., were discouraged by the results of their research. They concluded that their technique may be applicable to only a small percentage of prostate carcinomas, specifically those that are small and can be imaged by ultrasound. In their paper, they emphasized their concern for preventing RF heat damage to the rectal mucosa tissue. Thus, as a result of their efforts to treat prostate cancer, which is predominantly located in the peripheral non-central part of the prostate, they focused their research efforts on the peripheral, peri-rectal regions of the prostate. Their research did not contemplate RF ablation in the central periurethral region to produce an ablation cavity near the urethra or to ablate the urethra itself. In fact, they explicitly sought to avoid injury of the urethra by avoiding treatment of periurethral tissues. Their method and objectives were directed to cancer and were found to be disadvantageous for treatment of BPH or for treating urethral or periurethral tissues by radio-frequency (RF) ablation to relieve urinary obstruction.
It should be recognized that the theory behind and practice of RF heat lesion has been known for decades, and a wide range of RF generators and electrodes for accomplishing such practice exist. For example, equipment for performing heat lesions is available from Radionics, Inc., located in Burlington, Mass. Radio-frequency (RF) ablation is well known and described in medical and clinical literature. To that end, a research paper by E. R. Cosman, et al., entitled xe2x80x9cTheoretical Aspects of Radio-frequency Lesions in the Dorsal Root Entry Zone,xe2x80x9d Neurosurgery, vol. 15; no. 6, pp. 945-950 (1984), describing various techniques associated with radio-frequency lesions, is incorporated herein by reference. Also, a research paper by S. N. Goldberg, et al., entitled xe2x80x9cTissue Ablation with Radio-frequency: Effect of Probe Size, Gauge, Duration, and Temperature on Lesion Volume,xe2x80x9d Acad. Radiol., vol. 2; pp. 399-404 (1995), describes techniques and considerations relating to tissue ablation with radio-frequency energy.
In addition, a paper by S. N. Goldberg, et al., entitled xe2x80x9cHepatic Metastases: Percutaneous Radio-Frequency Ablation with Cooled-Tip Electrodes,xe2x80x9d Radiology, vol. 205, no.2, pp. 367-373 (1997), describes various techniques and considerations relating to tissue ablation with radio-frequency electrodes having cooled electrode tips. Cooled ablation electrodes will maintain tissue near the electrode at lowered temperatures which are below ablation temperatures. Cooling of the urethra by a catheter is suggested by McGahan et al., cited above, to prevent RF heat damage to the urethra and periurethral tissue.
Generally, cooled radio-frequency electrodes having an elongated shaft or catheter structure have cooling channels within the electrode structure. These cooling channels, for example, may comprise a first channel to carry cooled fluid from an external source, which is connected to the electrode at its proximal end. The coolant fluid is carried through the first channel to provide cooling to the electrode end, which is typically near the distal end of the electrode structure. The electrode structure typically also comprises a second channel within the electrode structure that is connected near the distal end to the first channel and which is adapted to bring the cooling fluid from the distal electrode region back to the source. Such recirculating channels for cooling fluid move the cooled fluid in one direction from the fluid source to the electrode and then back to the source. For a self-contained, internally cooled, electrode structure, the cooling channels would be inside the structure and sealed from other channels that may exist within the catheter such as for urinary drainage or for inflation of a balloon tip. Thus cooled electrode structures add a complexity of structure compared to non-cooled electrode structures.
Use of cooled ablation devices placed inside the urethra would have the objective of sparing the urethra from heat damage during the time when heating of prostatic tissue is occurring at a distance from the urethra.
Transurethral microwave thermotherapy (or xe2x80x9cTUMTxe2x80x9d) has been used to treat BPH and illustrates the use of a cooled catheter which also delivers heat energy to the prostate. A catheter which has a microwave probe inside it is inserted into the urethra to the point of the prostate. The microwave probe is typically a microwave antenna which is located inside the catheter near its distal end and is connected to an external generator of microwave power output. In this way the prostate is heated by radiative electromagnetic heating. At the same time the catheter is cooled by circulation of a coolant fluid within the catheter. The objective is, as stated above, to cool the urethra and thereby prevent damage to it by the heating process which is occurring in prostatic tissue that is outside of and at a distance from the urethra. Thus, the TUMT procedure seeks to preserve the urethra and the prostate tissue immediately outside the urethra by cooling the catheter with fluid coolant that is circulated within the catheter. In TUMT, the microwave antenna is located inside the catheter and not in conductive electrical contact with the urethra. The microwave heating in the TUMT procedure occurs in the prostatic tissue located at a distance away from the urethra as a result of the simultaneous cooling action of the channels within the catheter and the deposition of microwave power into the prostate tissue from the radiated energy from the antenna. Thus the prostatic tissue immediately around the urethra and the urethra itself are deliberately spared from receiving an ablative level of heating in the TUMT procedure. Further explanation of the TUMT system and procedure can be found in the paper by Blute, et al., entitled xe2x80x9cTransurethral Microwave Thermal Therapy for the Management of Benign Prostatic Hyperplasia: Results of the United States Prostration Cooperative Study,xe2x80x9d J. Urol., vol. 150, pp. 1591-1596 (1993).
Conventional techniques such as those described above have not been directed at creating ablation of urethra or the periurethral region (the region surrounding the urethra or the critical prostate region) for the reasons discussed above. The present invention is based, in part, on the realization that it would be desirable to have an effective technique to perform intra-urethral ablation of the urethra and periurethral tissue for the purposes of alleviating urinary obstruction caused by enlargement of the prostate and that avoids the limitations of the art (e.g., piercing the urethra).
The present invention is directed to a system and procedure for heat ablation of prostatic tissue through the use of a thermal probe that is advanced into the urethra through the penis and positioned intra-urethrally (within the urethra). The ablation is performed for the treatment of benign prostatic hyperplasia (BPH) and the associated alleviation of urethral obstruction. It would also be used for other diseases such as prostate cancer to relieve urethral obstruction. The system and procedure of the present invention are different from any of the systems and procedures discussed in the background section. The advantages of the present system and method reside in their combined simplicity, economy, control, consistency, enablement of good ablation position and shape, and clinical effectiveness.
As one example, urinary bladder outlet obstruction can be effectively treated using the present system and technique, which is minimally invasive. The technique of the present invention involves inserting a thermal probe into the urethra to the region of urethral obstruction in the prostate. The thermal delivery portion of the probe remains within the urethra. This avoids the more difficult and uncomfortable transurethral approach of the TUNA system procedure discussed above, and may be done without need for passing one or more side-outlet RF electrodes through the urethral wall (via a transurethral approach) into the prostatic tissue surrounding the urethra. In various embodiments, the present system and procedure may include image guidance, which may be performed in a variety of ways including ultrasound, CT, MRI, fluoroscopy, X-rays, or other well known imaging techniques.
In accordance with one embodiment of the invention, a thermal probe may comprise a flexible rubber urethral catheter having an inflatable balloon tip and urinary drainage channel. A thermal heating element comprising a resistive heating element is attached to the catheter proximal to the balloon portion. This heating element can thermally contact the urethral tissue when the catheter is inserted through the penis into the urethra. The balloon may be inflated when the distal portion of the catheter is within the patient""s bladder thereby enabling the catheter and the heating element to be fixed in a desired position relative to the prostate and urethra. The heating element may be determined to be at a desired position in the prostate by a simple traction of the balloon on the bladder. This also ensures against migration or change of position of the electrode from its proper position relative to the prostate and critical structures. X-ray, fluoroscopic, ultrasound, CT, or MRI imaging information can be made of the position of the electrode within the prostate and urethra.
In yet another embodiment of the invention, the thermal heating element of a urethral catheter comprises a flexible thermal element that can flex to conform to the curves of the urethra for insertion. The thermal element may comprise, for example, a resistive heating element, an RF conductive surface element, a conductive segment of the catheter, or an electrode or radiating element that is curvable and flexible for comfortable insertion into the urethra.
An electrical connection is made from the heating element to a power generator external to the patient""s body. The output from the generator is used to heat and thus ablate the urethral tissue and surrounding prostatic tissue near the heating element location. This creates a cavity and expanded opening of the urethra to relieve the urinary obstruction caused by BPH or other prostatic disease.
In contrast to the TUNA technique, the thermal probe of the present invention can be used without piercing the urethra. It enables patients who cannot tolerate the TUNA system and procedure to receive urethral ablation treatment. For example, such patients could be those requiring anticoagulation medication for cardiac or neurological problems who should not risk bleeding from a punctured urethra.
In a technique performed according to the present invention, a thermal probe is made to ablate a portion of the urethra and the periurethral region (i.e., tissue near or on the urethral tube) to induce necrosis of the prostate tissue near the urethra and of the urethra itself. This induces a cavity to be formed via obliteration of a portion of the urethra and the central region of the prostate in the patient""s body a few days after the procedure is performed. The cavity provides direct communication to and widening of the urethral channel. In accordance with one embodiment of the invention, thermal ablation depths of several millimeters into the periurethral tissue can be made, which thereafter induce similar sized cavities to be formed, thereby enlarging the urethral passage. These exemplary lesion sizes, similar to those made by the TURP procedure, have proven to be adequate to provide relief from BPH.
It should be noted that in contrast to McGahan et al.""s conclusion that RF lesion sizes are inadequate for the ablation of prostate carcinomas, the periurethral ablation sizes are adequate in treating BPH. Periurethral ablation in accordance with the present invention may also be used to ablate cancerous tumors of the prostate that may be located in the region of the urethra.
Also, the present technique avoids the need to observe McGahan et al.""s admonition to avoid heat or thermal injury of the urethra, and corresponding necessity for the irrigation and cooling of the urethra as suggested by the article by McGahan et al. By ablating the urethra itself, the present technique has the added advantage of avoiding the possibility of necrotic tissue and liquid becoming entrapped outside the urethra if the urethra is left intact, as in the case of the TUNA and McGahan et al. procedures.
The system and procedure of the present invention differs from TUMT techniques which seek to preserve the urethra by fluid cooling within the electrode catheter. The present technique seeks to ablate a portion of the urethra and periurethral tissue and so directly widen the urethral channel. The present technique has the advantage over the TUMT technique of not requiring added coolant-carrying channels within the catheter which increase complexity and cost of the TUMT electrode systems. The electrodes of the present invention are also simpler than the TUMT devices. The present invention involves a simply constructed thermal probe that is in thermal contact with or in physical contact with the urethra as compared to an internally located and complex microwave antenna structure in the case of the TUMT device.
The system and method of the present invention has the further advantage of increased simplicity, safety, and economy. The probe structure may be of a simple construction and geometry in one form not requiring coolant channels (although other versions can be made with cooling channels). This has the advantage that the catheter and thermal probe are easy to construct and therefore economical. The probe can be inserted easily by any urologist or clinical assistant. Also, it is well tolerated by patients, even those who are in frail health. The systems and methods of the invention are safe. For example, the simple use of the embodiment of an inflatable balloon within the urethra combined with catheter traction and X-ray imaging with contrast injection assures the correct positioning of the thermal probe within the urethra and prostate.
These features and advantages as well as others of the present method and system will become apparent in the detailed description that follows.